In common color filters, a mesh-like light shielding, thin film layer called a black matrix is provided on a substrate, and colored, cured coating film layers which correspond to each colors were formed in each mesh in the black matrix and these meshes of each colors are regularly arranged therein, so that the three primary colors of light, that is, red, green and blue are selectively transmitted when the color filter is a transmission type, and the three primary colors of cyan, magenta and yellow are selectively reflected when the color filter is a reflection type. Note that each of the “mesh” of the above-mentioned black matrix is commonly referred to as a “pixel”.
Color filters have been used in color displays such as a color solid state imaging device, a color liquid crystal display, a color cathode ray tube (CRT) and the like. In recent years, as the color liquid crystal display panel has increased in size and has been used in a wide variety of applications, improvements in reliability have also been demanded for the color filters used therein in terms of color reproducibility, heat resistance, light resistance, chemical resistance or the like.
With respect to the method for producing a color filter, a staining method in which a dye is used as a colorant was popular initially. However, in order to meet the above demands, a pigment dispersion method using a pigment which is excellent in terms of heat resistance, light resistance, chemical resistance or the like has become popular in recent years. Among the pigment dispersion methods, a “photolithography method” has been widely used, a pigment-dispersed resist formed by adding a pigment dispersing composition in which a pigment is dispersed using a dispersant, a photopolymerizable monomer, and photopolymerization initiator to a binder, is coated onto a substrate and then dried, followed by an exposure process through a photomask, a development process and a thermal curing treatment, thereby forming a cured coating film layer of the pigment-dispersed resist in the pixel portion.
As a method for producing a color filter using the “photolithography method”, for example, a method has been proposed to produce a pigment dispersing composition for a color filter, which is excellent in terms of transparency, developability and light resistance as well as storage stability, by containing a pigment, a coupling agent, an acrylic copolymer having an N,N-disubstituted amino group and acidic group in the main chain or side chain thereof, and a solvent (for example, refer to Patent Document 1). However, even with the above method, the produced color filters do not necessarily satisfy the high requirements made in recent years in terms of the properties, such as the dispersion stability, long-term storage stability and transparency.
On the other hand, a method has been known in which a pigment dispersion for a color filter which is excellent in terms of dispersion stability, long-term storage stability, transparency or the like is obtained by kneading a general purpose pigment, a resin and an organic solvent using a planetary mixer while setting the solid content ratio between the pigment and the resin (based on mass) to a specified ratio and also removing the organic solvent through evaporation (for example, refer to Patent Document 2). However, since the above method involves a constant monitoring of the solid content ratio during the kneading process, and also requires a kneading for many hours because the process is a stiffening process, it is not a simple kneading method.
[Patent Document 1]: Japanese Unexamined Patent Application, First Publication No. 2003-64293 (paragraphs [0002] through [0008])
[Patent Document 2]: Japanese Unexamined Patent Application, First Publication No. 2006-111752